This application requests funds to purchase an Applied Precision DeltaVision OMX SR 3D Structured Illumination system (3D-SIM) to be installed in the Bio-Imaging Resource Center (BIRC) at The Rockefeller University in New York. The DeltaVision OMX SR (DV OMX SR) is one of the first commercially available "super-resolution" microscopes that permit's researchers to resolve biological components or structures at double the resolution, in all three axes, of that which can be achieved using any conventional microscope. Moreover, this improved resolution can be achieved with multiple colors simultaneously and in any type of sample up to 10-20 micrometers thick, rendering this a very flexible approach that can now be applied to address a number of important questions in biomedical research that were hitherto impossible to answer. The researchers who will initially benefit from this system work on a broad array of organisms and health-related issues, including: the role of telomere length in repressing DNA damage in mammalian cells (relevant to cancer and age-related diseases);the molecular basis for ensuring accurate segregation of replicated chromosomes during mammalian cell division (evaluating chemical inhibitors of components as drugs for cancer therapy);structural changes in the dendritic spines of neurons that occur during learning as well as in disease (Alzheimer's, schizophrenia, Parkinsonism);understanding the structure of Streptococcal bacteria and other pathogens;understanding the organization and dynamics of both yeast and mammalian nuclear pore complex proteins (also implicated in proper chromosome segregation during cell division, and known to be potent tumor suppressors);and elucidating the ordering of DNA replication sites in the eukaryotic nucleus (accurate copying of the genetic material being crucial for genomic stability and to avoid somatic genetic diseases such as cancer). All of these questions will be approached by the method of using fluorescent tags to locate the relative positions of proteins, molecules or macromolecular structures within fixed cells. Although this approach has already been applied, in all cases, the inability of even the high-end microscopes in the BIRC to distinguish between neighboring components that are closer together than 200 nm in the xy axis, or 500 nm in the z-axis, has severely limited the questions we can ask. We show here that preliminary experiments using the DV OMX SR system provided new biological information in all of our research areas, opening up new lines of scientific enquiry that are presented below. The requested system will be housed in a large and well-supported core facility in a central location in New York, which offers access to numerous outside researchers as well as the named users and other RU investigators.